Insulated sectionalized bus duct system



April 1, 1952 N. SWERDLOW EI'AL 2,591,386

INSULATED SECTIONALIZED BUS DUCT SYSTEM Original Fil ed Aug. 51, 1948 Inventors I Nathan SwewclLow, A George 61. AbeL,

by W

Their" Attorney.

Patented Apr. 1, 1952 INSULATED SECTIONALIZED BUS DUCT SYSTEM Nathan Swerdlow, Philadelphia, and George G. Abel, Media, Pa., assignors to General Electric Company, a corporation of New York Original application August 31, 1948, Serial No.

47,128. Divided and this application Novemher 1, 1949, Serial No. 124,925

Claims.

This invention relates to enclosed electric bus installations and more particularly to an insulating mounting arrangement for electric bus systems of the isolated phase type. This application is a divisional application of pending application Serial No. 47,128, filed August 31, 1948.

In bus installations such, for example, as are used in high capacity electric power generating stations, it is vital that a high degree of reliability be achieved in order that outage time may be minimized and, furthermore, it is desirable that all the parts of the bus system be arranged so as to be readily accessible for testing, inspection, and repair, if necessary, so as further to minimize undesirable outage time.

One object of our invention is the provision of supporting structure for a bus run of the isolated phase type which is capable of minimizing circulating currents induced in the sheath due to the flow of current through the bus and which structure lends itself to simple yet reliable testing procedures.

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of our invention, reference may be had to the accompanying drawings in which Fig. 1 is a side view of a portion of a generating station showing the generator and a sectionalized bus run comprising the representative units designated by the numerals 2 through 9; Figs. 2 and 3 represent a particular construction whereby the various units, such as 2 through 9 of Fig. 1, may be insulated one from the other and also from ground except at a particular point of connection to a ground bus; and Fig. 4 represents a modification of the construction shown in Figs. 2 and 3.

With reference to Fig. 1 the numeral 1 designates a station power generator which is con nected to a sectionalized bus run only one phase of which, for convenience, is shown. The units 2 through 9, comprising the single phase bus run, are supported by means of suitable I-beams l5 which in turn are secured to the station ceiling, walls, or other suitable supporting structure in any convenient manner, which is not shown. The sections or units 2 through 9 are factory assembled andall are alike in that they terminate at their respective ends in a projecting cylindrical flange II. When the various units 2 through 9 have been mounted in their predetermined positions in the station, they may then be connected together at each junction by a clamping band I2 which embraces the separated flanges II. It will be understood that various combinations of the units 2 through 9 collectively constitute a conducting bus disposed axially within a squaresectioned box-like metallic sheath and that the conducting members therein are supported on insulators within the sheath. For a bus of high current carrying capacity, the sheath preferably is constructed of suitable non-magnetic material, such as aluminum.

It will be further understood that in such a station bus arrangement, longer bus runs than that depicted for illustration in Fig. 1 would usually be involved; accordingly, the major portion of the total length of the bus would be constituted by a number of standard units of some predetermined convenient short length of several feet. The numerals 4, l, and 9 indicate typical identical units, and it will be observed that such standard straight units may be mounted Vertically, horizontally or in any position for which suitable mounting structure has been provided.

The component parts of the standard units are such that they are readily adaptable for use with units possessing forms different from the straight type, such as, for example, the angle units indicated by the numerals 2, 3 and 5. Also, the rectangular box-like bus sheath with its short cylindrical end flanges lends itself readily to special purpose adaptations thereof such as will hereinafter be described.

The structure thus far described comprises a continuous single-phase bus run made up of segmental portions or units. The various adjoining units might be insulated from each other longitudinally of the bus by means such as sealing rings interposed between the clamping bands l2 and the flanges II, which rings are effective for limiting the flow of undesirable induced longitudinal circulating currents as is well known in the art. If the sheath of each unit of the bus is grounded by virtue of a bolted connection to the I-beams I0 which ordinarily are connected to ground, circulating currents might not flow through the junction between adjoining units, but by virtue of the ground connection made at two points on each unit, the ability of induced currents to circulate through each sheath via the two grounded points will produce objectionable heating. This circulation may be prevented by insulating the sheath at one of its two points of support by any well known manner. With such an obvious arrangement, however, it would be impossible to determine as by a bell set whether the insulating seal ring between two adjoining units was efiective as an insulating means or not because, if a test connection were made to one unit's sheath through a battery and a bell to the sheath of an adjoining or any other unit, the bell would ring in any event because of the parallel circuit afforded by the grounded structure via the mounting of the uninsulated I-beam of each bus unit.

If, however, each bus unit were entirely insulated from the grounded supporting structure, so that grounding were possible only through an isolated ground or test bar connected to each unit, the above-mentioned bell test could be applied effectively, providing the ground bar of one of the units involved were disconnected (or not yet connected) to the common ground bus associated therewith. Figs. 2 and 3 illustrate a practical application of this concept wherein the sheath I3 of each unit is entirely insulated from the I-beams I017 and I00, and, because the ground bar I4 is also insulated from the I-beams, the only possible electrical path from the sheath to the common ground bus 2I which parallels the run is that via the bar I4. In a preferred construction, the I-beam Ic has permanently mounted thereto, but insulated therefrom, a mounting bar I in addition to a ground bar I4. A projecting, upturned end of the ground bar I4 is detachably secured to the ground bus 2| by the bolts I6. The bolts I'I secure the mounting bar I5 and ground bar I4 to the I-beam I0c without forming an electrical path therebetween because of the provision of insulating washer I8 and insulating sleeve I9. Insulating strip 20, clamped between the I-beam I00 and the ground bar I4, prevents any current fiow from the sheath I3 to the beam I00; and the mounting bar I5 can be regarded as a permanent fixture to the I-beam I0c but insulated therefrom. Thus, from Fig. 3 particularly, it will be seen that the sheath I3 and parts connected therewith can be grounded only through the mounting bar I5, the ground bar I4, and the ground bus 2|. It will further be understood that an insulated structure similar to that shown in Fig. 3 would be used in connection with the other I-beam I0b of the unit of Fig. 2, except that instead of the ground bar I4 which connects to the bus 2I, a metallic spacer bar Nb of the same thickness as the ground bar would be used. This bar I4b does not extend beyond the ends of the I-beam for its sole function is that of a spacer of equivalent thickness to the ground bar. An insulated bus unit as described above would be secured to the beam structure by main mounting bolts 22. For preventing inadvertent electrical contact between the edges of the jointing straps I2 with either of its associated units, thin auxiliary insulation strips 23, which may be cemented to the end members II, preferably are employed, and sealing rings 24 render the enclosure dust tight.

From the above description, it will be clear that the only electrical path possible from the sheathed structure of a unit is via its ground bar I4 so that, if a bell set were connected to the sheath I3 of Fig. 2 and to a similarly constructedadjoining sheath section, it would test the insulation comprising the rings 24 and the strips'23 provided that the ground bar I4 of one of the units were disconnected from the ground bus 2| by unbolting the bolts I 6 and by separating the ground bar I4 from the ground bus 2|. In such a test, the bell would not ring if the insulation were sound.

Fig. 4 shows an alternative arrangement for securing a mounting bar I50, insulatingly to an I-beam such as I00. In this construction, an insulating strip or strips 25 are disposed around the lower fiange of the I-beam thereby isolating it electrically from the mounting and ground bars. The mounting bar I50, which is appropriately wider than the bar I5 is secured to the I-beam by means of bolts 26 and clamps 21 and, as will be seen from Fig. 4, the insulating strip 25 extends around the edges of the I-beam in such a way as to insulate the clamps 21 and bolts 26 therefrom. The arrangement of Fig. 4 makes it unnecessary to drill holes through the I-beam and, furthermore, dispenses with the insulating sleeves I9 of Fig. 3 and the insulating washers I8, best shown in that figure.

Although the foregoing detailed description has dealt with a single-phase bus run for simplicity, it will be understood that three-phase bus is more commonly employed in practice. In such cases, it will be readily appreciated that three identical single-phase bus units would be disposed in close side-by-side relationship which would depend from a pair of common I-beams I0 extending across the collective breadth of the three units.

While we have shown and described particular aspects of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention and we, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an isolated phase bus run having an enclosing sheath for each phase conductor andconstructed of a plurality of unitary structures each including an enclosing sheath, a first supporting means mounted exteriorly of and adjacent to each of said structures, a ground bar and a first mounting bar secured to said first supporting means and insulated therefrom, means for securing each of said structures to the adjacent first mounting bar, means for removably connecting said ground bar to a-grounded ground bus, a second supporting means mounted exteriorly of and adjacent to each of said structures, a second mounting bar and a spacer member secured to said supporting means and insulated therefrom, means for securing each of said structures to the adjacent second mounting bar, and means for forming a insulating junction between the sheaths of adjacent unitary structures for minimizing the flow of circulating currents in said sheaths.

2. In an isolated phase bus run having an onclosing sheath for each phase conductor and constructed of a plurality of unitary structures each including an enclosing sheath, a first supporting means mounted exteriorly of each of said structures, a ground bar and a first mounting bar secured to said first supporting means and insulated therefrom, means for removably connecting said ground bar to a grounded ground bus, a second supporting means mounted exteriorly of each of said structures, a second mounting bar and a spacer member secured to said supporting means and insulated therefrom, bolting means disposed within openings in each of said structures which are of substantially greater diameter than the diameter of said bolting means for securing said structures to each of said mounting bars, 50 that said structures may be assembled without the necessity of precisely positioning said first and second supporting means, and sealing means of insulating material for forming a weather-tight junction between the sheaths of adjacent unitary structures and for preventing the flow of circulating currents between such junctions.

3. In an isolated phase bus run having an enclosing sheath for each phase conductor generally comprising a plurality of unitary structures each including an enclosing sheath member, a first supporting means mounted exteriorly of each of said structures, a ground bar and a first mounting bar disposed between each of said structures and each of said first supporting means, a first layer of insulating material disposed between each of said first supporting means and said ground bar and having a portion thereof extending around another surface of each of said first supporting means, means for removaoly connecting said ground bar to a grounded ground bus, a second supporting means mounted exteriorly of each of said structures, a second mounting bar and a spacer member disposed between each of said structures and said second supporting means, a second layer of insulating material disposed between each of said second supporting means and said spacer member and having a portion thereof extending around another surface of each of said second supporting means, means cooperating with each of said mounting bars and each of said supporting means and engaging said portion of each of said insulating layers for removably securing said first and second mounting bars to said first and second supporting means, means for removably securing each of said structures to said first and second mounting bars, and sealing means of insulating material for forming a weather-tight junction between the sheaths of adjacent unitary structures and for preventing the flow of circulating currents between such junctions.

4. In a sectionalized isolated phase bus run comprising a plurality of similar sheathed units, plural mounting means for ri idly connecting each said similar unit to a supporting structure, insulating means interposed at each said mounting means for precluding current flow therethrough from said unit to the supporting structure, a joint between each said unit for rendering the sheathing about said bus substantially continuous, insulating means at each said joint for precluding current iio'w between the sheaths of the conjoined units, a ground bar electrically connected to the sheath of each said unit, said ground bars being disconnectably attached to a common ground bus, whereby circulating currents in the bus sheath are minimized and the testing of the insulated joints of said units is facilitated by disconnecting said ground bars.

5. In a sectionalized isolated phase bus run comprising a plurality of similar sheathed units, means for mounting each said unit to a foundation structure and for conjoining it to an associated unit at its either end, means for electrically insulating each said unit from the said foundation structure and from its conjoined units, a ground bus, and a disconnectable ground connection conductively arranged between certain of said units and said ground bus whereby upon disconnection thereof said certain unit sheaths are rendered electrically isolated.

NATHAN SWERDLOW. GEORGE G. ABEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 960,066 Bluhm May 31, 1910 2,275,203 Rudd Mar. 3, 1942 2,313,972 Rugg et a1. Mar. 16, 1943 

